Envoy ACP/XF Application Programming Manual

Normal Response Mode (NRM) Protocols

EnvoyACP/XF Application Programming Manual–132179

3-31

NRM READ Procedure

Delaying I-Frame Acknowledgment

EnvoyACP/XF also supports an alternate procedure for I-frame acknowledgment.

You must use SCF to enable the alternate procedure specifying OPTION1. OPTION1

cannot be enabled through a SETMODE procedure.

When OPTION1 is enabled and a supervisor station receives an I-frame with the

poll-final bit set, the supervisor does not send back an RR-frame immediately to

acknowledge the received I-frame. Instead, the supervisor polls the other stations in the

poll list. The supervisor does not acknowledge the received I-frame until the polling

cycle comes back to the tributary station that sent the frame.

Figure 3-8. Standard I-Frame Acknowledgment

Note. When you use OPTION1, the primary station never sends an RR-frame without the

poll/final bit set.

048

Supervisor Station

(NR/NS)

01 RR–P

01 I–F

01 RR

(0)

(0, 0)

(1)

02 RR–P (0)

Legend

1 The supervisor station polls tributary station 01 by sending it an RR–frame

with the poll bit set.

2 Tributary station 01 responds by sending back an I–frame with the final bit set.

3 The supervisor station immediately acknowledges the I–frame by sending

another RR–frame with the sequence number for the frame number received

(NR) increased to 1.

4 The supervisor station then proceeds to poll tributary station 02.

5 Station 02 does not have any information to send, so it responds by sending

the RR–frame with the final bit set.

02 RR–F

01 RR–P

(0)

(1)

6 The supervisor's polling cycle is at station 01 again; the supervisor sends the

RR–frame to station 01 with the poll bit set, and the sequence number for the

frame number received (NR) remains at 1.

Tributary Stations